And this is not the first time, although in the past the DOJ did it directly.
For example, Kim dot Com had great difficulty finding US counsel to represent him. And he alleged that Brandon van Grack (of Team Mueller fame) had gone around DC telling every law firm to stay away from representing Kim dot Com , or face retaliation.
In the case of Trump it was social and professional pressure from almost the entire legal profession.
I'm sure you are right. When Trump was a citizen real estate developer, he had his pick of lawyers. But when you become the most dangerous man in the world, your enemies don't want you to be able to find competent representation, and will do whatever they need to, to keep you from finding any.